1. Field of the Invention
The present invention relates generally to a method for determining spark plug malfunction.
2. Background of the Invention
To ensure engine emission performance, it is desirable to perform testing of the engine during operation. An engine equipped with two spark plugs per cylinder provides a unique opportunity to detect a spark plug failure. According to U.S. Pat. No. 5,872,312, one of the two spark plugs in each cylinder in a bank of the engine""s cylinders is disabled. Stated another way, one half of the spark plugs in an entire bank are simultaneously disabled. If a misfire is detected during testing on the bank of cylinders, a spark plug of each cylinder is disabled in succession. In this way, it may be determined which spark plug is experiencing a malfunction.
The inventors have recognized a problem with the approach in U.S. Pat. No. 5,872,312 in that, if a spark plug is malfunctioning, two misfires occur in the process of identifying the malfunctioning cylinder, i.e., a first misfire occurs in the bank testing of cylinders and a second misfire in testing individual cylinders. Because a misfire may lead to hydrocarbon emission and may cause overheating of an exhaust catalyst, misfire occurrence should be minimized. The inventors of the present invention have recognized an alternative procedure to detect spark plug malfunction which overcomes the problem of multiple misfires.
Disadvantages of prior art approaches are overcome by a method for controlling and diagnosing a multi-cylinder internal combustion engine having two spark plug in each cylinder to determine spark plug malfunction by disabling one of the spark plugs during a test period in a particular cylinder. It is determined whether a misfire has occurred during the disablement, which provides an indication of malfunction of the other spark plug. During the test period, each spark plug is disabled only once.
An advantage of the present invention is that if a spark plug malfunction is occurring, it can be detected in one misfire occurrence. In prior art, two misfires occur in performing the detection scheme. Because misfires lead to short bursts of higher exhaust emissions and a large increase in catalyst temperature, the present invention provides a clear advantage in lower hydrocarbon emission and a lower potential for overheating and possibly melting a catalyst.
An additional advantage is that the present invention requires fewer processes to be undertaken to determine which spark plug is malfunctioning. The algorithm may be performed in a shorter period of time, thereby providing a more rapid identification of a malfunctioning spark plug.
According to another aspect of the present invention, a method for controlling and diagnosing a multi-cylinder internal combustion engine is disclosed in which an ignition spark is provided through a first spark plug positioned in one of the cylinders near a center axis of the cylinder and ignition spark is provided through a second spark plug positioned in the cylinder near a wall of the cylinder. The first spark plug is disabled during a test period in one of the cylinders and it is determined whether a misfire has occurred during the period that the first spark plug is disabled. A misfire provides an indication of a malfunction of the second spark plug. An advantage of this aspect of the present invention in providing smoother engine operation during the diagnostic procedure than prior art methods in engines with one of the spark plugs located near a cylinder wall and one of the spark plugs centrally located. When prior art approaches are used to diagnose the spark plugs located near a wall in a dual bank engine, the centrally located plug along an entire bank of cylinders are disabled simultaneously. Even if none of the spark plugs being diagnosed were malfunctioning, simply by performing the diagnostic procedure torque drops about 15% during the disablement due to the loss of combustion initiation in the dominant position, the central position. Such a torque drop would be noticeable and objectionable to the driver. The situation is even worse if the prior art diagnostic routine were performed on an engine with a single bank of cylinders. The present invention, in contrast, provides for diagnosing one cylinder at a time resulting in a torque loss of about 5% (in a 6-cylinder engine), which is well within the range of normal cycle-to-cycle torque differences.
The above advantages, other advantages, and other features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.